The possible downside of your genes
By Vejay Steede
It’s all in the genes. If you’re tall or dark-skinned or greeneyed, you’ve been given gifts from the genes you inherited from your parents. Not all genes are quite so generous, however, and some can even put you at risk for highly undesirable health conditions throughout your life. For example, what if your family has a history of cancer? Will you inherit genes that will eventually put you at a higher risk of contracting the most devastating blight of our age? This is a great (and justifiable!) fear for people with close relatives who have succumbed to cancer, and the statistics do show that certain specific genes can put offspring at risk for some cancers.
Kevin S. Hughes,
MD, FACS, is the Director of Cancer Genetics and Mc- Coy Rose Professor of Surgery in the Department of Surgery at the Medical University of South Carolina. He is also the Medical Director of the Bermuda Cancer Genetics and Risk Assessment Clinic and an esteemed Professor Emeritus at Harvard Medical School.
Dr. Hughes answered a few questions about genetic cancers and how testing for genes that may put individuals at risk of contracting cancer can dramatically affect survival rates if it is done correctly and in a timely manner.
Royal Gazette: What are the risks involved with genetic cancers?
Dr. Hughes: There are genes we get from our parents that help prevent cancer. If these genes have mutations that prevent them from functioning properly, patients are at higher risk of cancer. There are now over 80 cancer genes known, the most well-known of which are BRCA1 and BRCA2. Both markedly increase the risk of breast and ovarian cancer. Other cancer genes increase the risk of other cancers, such as colon or uterus.
If a person has a mutation in one of these genes, children of mutation carriers have a 50/50 chance of having the mutation. By doing genetic testing, we can identify who has a mutation and can then change the way they are screened and managed to help prevent cancer or find it at an earlier and more treatable stage. About five to 10 percent of cancers are caused by cancer gene mutations.
RG: Which cancers are most commonly passed on genetically?
KH: Breast, ovarian and colon are the most likely to be hereditary, but almost any cancer can have a hereditary component.
RG: Are any cancers more likely to show up in future generations than others? Are statistics available?
KH: Each gene has its own spectrum of cancers that it produces. You can go to http://ask2me.org to learn more about cancers and their statistics. As an example, a woman with no mutations has a 14 percent risk of cancer in her lifetime, while a BRCA1 carrier has about a 60 percent risk and an ATM carrier (which is another gene mutation) has about a 20 percent risk.
RG: Is testing for genetic cancers in children recommended?
KH: Seldom. Most hereditary cancers occur in adulthood, often in young adults, so testing before age 18 is seldom needed. However, some genes do cause cancer before age 18 (TP3, APC are two of these), and for these genes, testing before age 18 is useful.
That said, TP53 is a gene that is more likely to cause cancer in children, so that is something we test for in children. In addition, we know that childhood cancer is more likely to be genetic, so gene testing is done in children who contract cancer more than children who have cancer in their family. APC is a gene in children that causes colon cancer and requires colonoscopies to start as early as 10 to 15 years old in at-risk children.
RG: Please describe the testing procedures and result accuracy statistics for testing children for genetic cancers.
KH: Adult genetic testing is relatively routine and most providers can do this or learn how to do it. Testing children is much more specialised and there are tremendous social and psychologic overlays. This should be done at a centre with expertise in that gene and with the input of a genetic counsellor. If there is a very strong family history with a gene mutation found in a childhood cancer gene, that child should see a genetic counsellor and decide if testing is needed. If needed, it is usually a saliva or blood test. In addition, many children diagnosed with cancer should have genetic testing.
RG: Should persons who have cancer in their family be tested? If so, when and how frequently?
KH: Anyone with multiple relatives in the family with cancer, or cancer in the family at a young age (20s to 40s), or a family member with multiple cancers should discuss genetic testing with their doctor.
Many cancer patients also need testing regardless of family history. This includes any ovarian cancer, breast, colorectal or uterine cancer under age 50, for example. Genetic testing for cancer is usually done only once, but if a new test comes along, often the new test should be added. Cancer genetic testing before 2015 was likely only for a few genes, and now we test 30 to 100 genes routinely. Anyone tested before 2015 should likely have their testing updated.
RG: Is there any other important information on the topic of genetic cancers and genetic cancer counselling that the general public should know?
KH: This is a life’s work and hard to describe briefly, but I will try. The bottom line is that 90 percent or more of patients with mutations are unaware. Thus, they are not being screened as intensively as they should be. This means more advanced cancers occur than should happen. Also for some cancers, like ovary, the ovaries should be removed before cancer develops.
As patients are often not aware they have a mutation, they do not have their ovaries out and preventable ovarian cancers occur unnecessarily. We need more genetic testing before cancer develops. It is critical that genetic testing become much more routine and widespread in order to decrease the morbidity and mortality of cancer.